An apparatus for measurement of a conductor current which is flowing in an axially elongated electrical conductor at a first electrical potential is generally disclosed in WO 95/09447 A.
Current measurement is used throughout the entire field of electrical power transmission, power management, control engineering and automation engineering. Since this frequently relates to a safety-relevant function, the current transformer that is used must be protected against external disturbance influences and fields. If low-cost and geometrically simple solutions are available, the current monitoring can intervene at an early stage, and can prevent damage, at a large number of points.
Nowadays, various solutions exist for current detection and measurement, for example with measurement resistors (shunts) being used combined with opto couplers, as well as current transformers, Hall elements, field plates, sensor systems using magnetoresistive material, and fiber-optic current measurement devices. However, many of the current sensors have a limited operating range and are limited, for example by alternating-current measurement since they are based on inductive principles, or cannot be integrated. One problem of the magnetic solutions which have been mentioned, in which the field of a conductor through which a current passes is measured, results from the fact that a disturbance field frequently acts highly directly, and shielding devices or graded and/or compensation methods must be used all the time.
The WO-A document which was cited initially discloses a current measurement apparatus which has at least one sensor element which surrounds a conductor through which current flows, in the form of an open ring. In this case, the open ring is formed by a multilayer system composed of metallic magnetoresistive material of the so-called AMR (Anisotropic Magneto Resistance) type. The magnetoresistive material is made contact with at the adjacent ends of this ring, which form a slot, in order to tap off the resistance value. A sensor element such as this may be connected to further elements which are not sensitive to magnetic fields, to form a bridge. The magnetoresistive materials which are used can be produced in curved shapes, such as the slotted annulus that is required, only with considerable effort.
DE 39 29 452 A1 likewise discloses a current measurement apparatus. The known apparatus contains a magnetic field ring sensor, which has a substrate with a central circular opening for an electrical conductor to pass through. A large number of individual sensor elements of the so-called barber pole type are arranged around the circular opening and each have strips which are deposited on the substrate using a thin-film technique, are aligned radially, are composed of magnetoresistive material and have electrical conductor parts running at an angle to them. The individual sensor elements, which are considerably separated from one another in the circumferential direction, are electrically connected in series. The design of this known apparatus is highly complex.